Imagine a car race about to take place. A car is starting at rest and when the timer goes off, the driver steps on the gas. The car starts off so fast, that its front wheels rise upwards so that all the weight of the car is held up by the 2 rear wheels. The car travels this way for a few seconds. During the time which the car is on its two rear wheels, is the force of friction from the ground assisting the car's forward movement or opposing it?